One thing I am not quite some of what you meant is the "It drains more and more of the power after each cut." part. Do you mean that each time it connects it makes the enemy more unable to use his DF powers, or is this the standard seastone ability of negating the user's DF power upon, and as long as it lasts, contact?
Otherwise it's good to go, just specify me that so I know, as seastone doesn't work in a draining way, without actual continuous contact. Unless if I got it wrong, or if this sword has some other mechanic going on here.